Conventionally, some lighting apparatuses such as a vehicle lamp or optical apparatuses such as a surveillance camera are provided with a ventilation member for providing ventilation to the housing, in order to prevent deformation or breakage of the housing due to difference in pressure between the inside and the outside of the housing. When the housing is provided with the ventilation member, water vapor and the like may enter the housing through the ventilation member, which may lead to problems such as dew condensation inside the housing and fogging of a lens.
In view of the above, Patent Document 1 discloses a technique of filling the inside of a housing with a moisture absorbent such as silica gel to prevent fogging of a lens of an automobile lamp.